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Permalink How can I organically control cutworms?

B.C.
Minnesota

Answer: Thank you for your recent request for information from ATTRA, the National Sustainable Agriculture Information Service. I am pleased to provide you with information about cutworm and organic/ biorational control methods.

Cutworms wreak havoc during seedling and transplant establishment. Problem areas are usually found near field borders and in weedier areas. Serious losses are often associated with wet springs that have caused a delay in planting.

Cutworm species include the variegated cutworm, Peridroma saucia; black cutworm, Agrotis ipsilon; granulate cutworm, Feltia subterranea; army cutworm, Euxoa auxiliaries, and claybacked cutworm, Agrotis gladiaria. They are active at night, feeding and chewing through the stems of the seedlings. In the day they burrow underground or under clods to avoid detection. To inspect for cutworms, dig around the damaged areas during the day or come out at night with a flashlight to catch the culprits in the act. Under resources you will see a link to the Purdue University IPM web site. It has close-up color pictures of each type of cut worm. This will give you an idea of the different species and help you correctly identify them. In controlling and preventing cutworm, it is only important to know whether or not the larvae over winter (see cultural control measures below) so that you know when to time cultural and control measures.

Most overwinter as larvae in “cells” in the soil, in crop residues, or in clumps of grass. Feeding begins in spring and continues to early summer when the larvae burrow more deeply into the soil to pupate. Adults emerge from the soil one to eight weeks later, or sometimes overwinter. Most species deposit eggs on stems or behind the leaf sheaths of grasses and weeds. Eggs hatch from two days to two weeks later.

In some crops, cutworms can be extremely damaging where transplants are planted through plastic. It has been reported that the increased heat radiating out at night, particularly around the bases of the plants, attracts the larvae to the plants. Once underneath the plastic, the larvae are very difficult to control.

Cutworms have many predators and parasites that can help control their numbers. Some of these parasites and predators can be purchased or harnessed naturally through planting or conserving habitat for them.

The potential for cutworm infestations is governed in large part by the following factors:
• Planting time
• low-damp areas of the field that drain poorly,
• fall and early season weed growth, and
• the amount of surface residue.

Cultural Controls
Cutworms are a particular problem in crops that follow sods, pastures, or weedy fields in rotation. Because infestations often begin on weeds, cultivation and other weed-control programs implemented directly before planting time may increase cutworm feeding on seedling crops. Clean tillage to remove all weedy vegetation, at least ten days prior to planting, reduces the number of cutworm larvae. Control of weedy vegetation, at this same time, at field borders also reduces the number of invading larvae.

To control cutworms that overwinter as partially grown larvae (claybacked and variegated) land should be kept weed-free, particularly of broadleaf weeds, during the fall months to reduce egg-laying by cutworm moths. A small grain cover crop, such as oats that winter kill, may cut weed competition and is more in line with the principles of organic production. Crops planted on sod are prone to cutworm damage unless the land is plowed in early fall and kept weed-free for the rest of the season.

Biological Controls
Cutworm larvae have a number of natural enemies. Predators include several species of ground beetles. Parasitoids include tachinid flies and braconid wasps. Cutworms may also be attacked by fungi, bacteria, and nematodes. Understanding the biology of beneficial organisms is imperative in order to use them effectively as pest control agents. For example, insect parasitic nematodes like Steinerema carpocapsae or insect-infecting fungi like Beauveria bassiana require adequate humidity to be effective. Other predators include spiders, minute pirate bugs, damsel bugs, and lacewing larvae. Birds also prey on cutworms, so do not assume that the birds in the field are causing the seedling damage. As with other pests discussed, farmscaping is a recommended means of increasing the numbers of beneficial predators and parasites that help to keep cutworms under control. In the resources section I have listed an ATTRA publication that is a good starting point for biointensive IPM, titled Biointensive Integrated Pest Management. There is a direct link to this publication.

Alternative Pesticides & Applications
Scout for the presence of cutworm larvae early in the season, and after destruction of adjacent habitats. Cutworms are best scouted at night, when they are most active, using a flashlight. Look for cut-off or damaged seedlings and dig around the base of the plant to locate the larvae.

Bait formulations, sometimes using bran or applying rolled oats with molasses, containing Bacillus thuringiensis var. kurstaki have been known to effectively control cutworm species when applied to the soil. Sprayed formulations may have variable results with cutworms, as the worms may not ingest enough of the toxin for it to be effective. Nightime spraying of Bacillus thuringiensis has shown to be more effective.

Research on the parasitic nematode species, Steinernematidae carpocapsae, has shown it to be a very successful control agent for cutworms, but make sure that the soil is sufficiently moist to support nematode populations (see above). I have attached to this letter a publication titled Integrated Pest Management of Greenhouse crops. While this publication is not relevant to cutworm specifically, it does list suppliers of beneficial organisms in its appendix section.

If natural pesticide applications are necessary, choose one that is least disruptive to the natural enemies. Early detection and application during the early developmental stages of the larvae (first and second instar) make these biorational pesticides more effective. For cutworm species that overwinter as larvae, this would happen in the early spring when the soil is warming. Pheromone traps will indicate when mating flights are occurring, and through degree-day calculations one can estimate egg laying and hatching. For information on degree-day calculations contact your local Extension agent. If you are truly sure that you have the black cutworm then you will want to time the Pheromone traps in the early spring to monitor when they migrate to your region. It is at this time you will be able to determine when they are in the 1st and second instar stages for most effective control with Bt and nematodes. Work with your local extension agent to determine the degree day calculations for cutworm in your area. Below under resources there is a link to places to purchase pheromone traps.

Resources:

Ruth Hazzard, Brian Caldwell, Eric Sideman, Vern Grubinger. June 17, 2004. Cutworm Management. Excerpted from University of VT Cooperative Extension Newsletter Vegetable and Berry News.

Anon. Purdue University IPM Guide. Cutworm: Multiple Species. 2006

Sources of Pheromone Traps:
Great Lakes IPM:
10220 Church Road NE, Vestaburg MI 48891
phone (517) 268-5693 or (517) 268-5911; fax (517) 268-5311
e-mail: glimpm@nethawk.com

Gempler’s:
P.O. Box 270, Belleville WI 53508
phone 800-382-8473; fax 800-551-1128

Dufour, Rex. Biointensive Integrated Pest Management (IPM)- Part One of Two
ATTRA Publication #IP049 . July 2001.

References:
Kuepper, George. Organic Field Corn Production. ATTRA Publication # CT113. January 2002.

Bessin, Ricardo. Cutworm Management in Corn. Publication # ENT-59. University of Kentucky Extension.
http://www.ca.uky.edu/agc/pubs/ent/ent59/ent59.htm

Advisory Service. September 2002.

Flint, Mary Louise. 1990. Pests of the Garden and Small Farm. University Of California, Oakland, CA. 276 p

Buhler, W.G. and T.J. Gibb. 1994. Persistence of Steinernema carpocapsae and S. glaseri (Rhabditida: Steinernematidae) as measured by their control of black cutworm (Lepi- doptera: Noctuidae) larvae in bentgrass. Journal of Economic Entomology. Vol. 87, No. 3. p. 638-642.

Ellis, Barbara W. and Fern Marshall Bradley. 1992. The Organic Gardener’s Handbook of Natural Insect and Disease Control. Rodale Press, Emmaus, PA. 534 p.

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